A Basic USe EDitor for gentoo. drop abused.py into your path, and use it in place of emerge when doing installs. It will allow you to edit your use flags on the fly.

abused.py

#!/usr/bin/env python

import os
import re
import sys
import string
import subprocess

class Abused:

    def __init__(self, args):
        if args:
            self.args = ' '.join(args)
        else:
            self.args = ''
            
        self.pcmd     = 'emerge -pv --color y'
        self.rcmd     = 'emerge -v --quiet-build --color y'
        self.flags_d  = []
        self.flags_c  = []
        self.pkglines = []
        
        # pretend so we can see the use flags
        print 'Examining USE flags...'
        self.__getUse()

        # display the current USE flags, and allow some editin
        while not self.__editor():
            pass

        # and fire off the real emerge
        self.__doEmerge()

    def __sanitize(self, data):
        retv = ''
        if data.find('\x1b') != -1:
            tmp = filter(lambda x: x in string.printable, data)
            retv += re.sub('(\{|\})', '', re.sub('\[[0-9\;]+m', '', tmp))
            return retv
        return False
    
    def __getUse(self):        
        cmd_s = 'USE="%s" %s %s' % (
            ' '.join(self.flags_c),
            self.pcmd,
            self.args
        )
        cmd_p = subprocess.Popen(
            cmd_s,
            stdout=subprocess.PIPE,
            stderr=subprocess.STDOUT,
            shell=True,
            executable="/bin/bash"
        )

        self.pkglines  = []
        self.flags_d   = []
        self.flags_c   = []
        self.longest_c = ''
        self.longest_n = 0
        
        buff = cmd_p.stdout.readline()
        while buff:
            if buff.strip().find('USE="') != -1:
                self.pkglines.append(buff.strip())
                flags_t = buff.strip().split('USE="')[1].split('"')[0].split()
                for f in flags_t:
                    if f not in self.flags_d:
                        self.flags_d.append(f)
                        if len(f) > self.longest_n:
                            self.longest_n = len(f)
                            self.longest_c = f
            buff = cmd_p.stdout.readline()

        # And build our sanitized list of use flags
        for f in self.flags_d:
            t = self.__sanitize(f)
            self.flags_c.append(t)

    def __editor(self):
        print
        for l in self.pkglines:
            print l
        print
        a = 0
        for i in self.flags_d:
            eval("sys.stdout.write('%%%ds' %% i)" % (self.longest_n+1))
            if a < 4:
                a += 1
            else:
                print
                a = 0

        sys.stdout.write("\n\n")
        sys.stdout.write('>> ')
        sys.stdout.flush()
        
        data = sys.stdin.readline().strip().split()        
        if len(data) == 0:
            return True
        else:
            # go through and replace the flags that are edited
            for f in data:
                for ix in range(0, len(self.flags_c)):
                    if self.flags_c[ix].find(f[1:]) != -1:
                        if f[0] == '-' and self.flags_c[ix][0] != '-':
                            tt = self.flags_c[ix]
                            self.flags_c[ix] = '-%s' % tt
                        elif f[0] != '-' and self.flags_c[ix][0] == '-':
                            tt = self.flags_c[ix][1:]
                            self.flags_c[ix] = tt
            # then refresh the data
            self.__getUse()
            return False

    def __doEmerge(self):
        cmd_s = 'USE="%s" %s %s' % (
            ' '.join(self.flags_c),
            self.rcmd,
            self.args
        )
        cmd_p = subprocess.Popen(
            cmd_s,
            stdout=subprocess.PIPE,
            stderr=subprocess.STDOUT,
            shell=True,
            executable="/bin/bash"
        )
        buff = cmd_p.stdout.readline()
        while buff:
            sys.stdout.write(buff)
            sys.stdout.flush()
            buff = cmd_p.stdout.readline()
    
if __name__ == '__main__':
    try:
        app = Abused(sys.argv[1:])
    except KeyboardInterrupt:
        sys.exit(1)